A diverging lens of focal length 30cm produces ... - WAEC Physics 2013 Question
A diverging lens of focal length 30cm produces an image 20cm from the lens. Determine the object distance
A
10cm
B
12cm
C
50cm
D
60cm
correct option: b
\(\frac{1}{v} + \frac{1}{v} = \frac{1}{f}\)
For a diverging lens, v is -ve, so we have
\(\frac{1}{u} - \frac{1}{v} = \frac{1}{f}\)
\(\frac{1}{u} = \frac{1}{f} + \frac{1}{v}\)
= \(\frac{1}{30} + \frac{1}{20} = \frac{2 + 3}{6}\)
u = \(\frac{60}{5} = 12cm\)
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